The present invention, in some embodiments thereof, relates to an electrospun scaffold comprising polymeric nanofibers and particles and, more particularly, but not exclusively, to the use of same for bone or connective tissue regeneration.
The need for bone repair is one of the major concerns of regenerative medicine. The key step in the modern approach of bone tissue engineering is the design and fabrication of porous three dimensional (3D) scaffolds. These 3D scaffolds serve as temporary artificial extracellular matrices, accommodating cells and supporting three-dimensional tissue regeneration. In order to achieve these goals, the scaffold's surface chemistry must be suitable for cell attachment and the pore size must allow cellular proliferation. The design of scaffolds that mimic the biological functions of the extracellular matrix, without eliciting an immunological reaction, is a major challenge in tissue engineering and bone repair.
Various applications utilizing scaffolds for tissue engineering and bone repair have been previously described, some are summarized infra.
Hydrogel scaffolds were demonstrated to provide biodegradable 3D structures, which promote cell growth and differentiation. Srouji et al. have demonstrated that these scaffolds promote osteogenic differentiation of bone marrow mesenchymal stem cells (MSCs) [Srouji et al., Microsc Res Tech. (2005) 66(2-3):132-8.]. Hydrogel scaffolds impregnated with growth factors have also been contemplated for treatment of bone defects. For example, bone morphogenetic protein-2 (BMP-2) [Yamamoto et al., J Biomater Sci Polym Ed. (1998) 9(5): 439-58], transforming growth factor beta-1 (TGF-beta1) [Yamamoto et al., J Control Release. (2000) 64(1-3): 133-42] and Insulin-like Growth Factor-1 (IGF-1) [Srouji et al., Cell Tissue Bank. (2004) 5(4):223-30] were all shown to enhance bone regeneration and healing.
PCT Publication No. WO06036826 discloses tissue engineering scaffolds for in vitro and in vivo use (e.g. for drug delivery or for supporting cell attachment and growth). These scaffolds comprise a nanofibrous, nanoporous hydrogel formed from self-assembling peptides. The peptides comprising the hydrogel may be biodegradable materials, include ceramics (e.g. hydroxylapatite), biodegradable polymers, including polycaprolactone (PCL) and polylactic acid (PLA), or non-biodegradable materials (e.g. silk). Furthermore, these scaffolds comprise cells (e.g. stem cells, progenitor cells).
U.S. Pat. No. 7,122,057 discloses use of engineered regenerative biostructures (ERB) as a bone substitute. These biostructures comprise ceramic materials (e.g. hydroxylapatite) that are partially joined to each other in a manner that leaves some porosity therebetween. According to U.S. Pat. No. 7,122,057, the micro- and meso-architecture of the ERBs is designed to be consistent and defined. Furthermore, the ERBs may comprise cells (e.g. MSCs ) or polymers (e.g. PLA and PCL).
Another approach for designing 3D porous scaffolds for use in tissue engineering is electrospinning. Electrospinning is a process that uses an electric field to control the formation and deposition of polymers. This process is remarkably efficient, rapid, and inexpensive. In electrospinning, a polymer solution or melt is injected with an electrical potential to create a charge imbalance and placed in proximity to a grounded target. At a critical voltage, the charge imbalance begins to overcome the surface tension of the polymer source, forming an electrically charged jet. The jet within the electric charge is directed toward the grounded target, during which time the solvent evaporates and fibers are formed. Electrospinning produces a single continuous nanofibrous filament that collects on the grounded target as a non-woven fabric.
Electrospinning yields scaffolds with a high porosity. The nanometer to micrometer fibers comprised therein combine in non-woven networks resembling the natural extracellular matrix. Because a collector is used that has the desired shape of the scaffold, complex scaffold geometries can be utilized. Moreover, in the electrospinning process, many parameters can be altered to optimize the properties of the final product.
Many different polymers have been previously contemplated in electrospinning; these include several classes of biomaterials such as synthetic polymers (organic and inorganic), ceramics and native polymers. Furthermore, the polymers can be biodegradable or non-degradable.
PCL scaffolds, produced by electrospinning, were reported to provide biocompatible structures for osteogenesis [Yoshimoto et al., Biomaterials (2003) 24: 2077-2082] and for chondrogenesis [Li et al, Biomaterials (2005) 26: 599-609]. Other synthetic polymers, such as polyglycolic acid (PGA) and poly(Lactide-co-Glycolide) (PLGA), and natural macromolecules, such as collagen and fibrinogen, have been processed into fibrous non-woven scaffolds for tissue engineering research [Li et al., J Biomed Mater Res. (2002) 60(4):613-21; Yoshimoto et al., Biomaterials. (2003) 24(12):2077-82].
Electrospun scaffolds fabricated from both synthetic polymers (such as polycaprolactone (PCL) and poly (lactide-co-glycolide; PLGA)) and natural polymers (such as silk and collagen) containing nanoparticles of calcium carbonate (CaCO3) or hydroxylapatite (HA) have been successfully used as bone scaffolding materials—see for example [Wutticharoenmongkol P. et al., J Nanosci Nanotechnol. (2006) 6(2):514-22; Li et al., Biomaterials (2006) 27:3115-3124; Venugopal et al., J Mater Sci: Mater Med (2007) Epub; Nie and Wang, J Controlled Release (2007) 120:111-121 and U.S. Publication No. 20050112349].